Fix appVolumeAdjuster when state is default (#17321)
Fixes #17300
Summary of the issue:
When AppVolumeAdjuster state is set to default, pressing OK or Apply button in settings sets the volume of all apps to 100%.
Description of user facing changes:
Bug fixed. Now when AppVolumeAdjuster state is set to default, application volumes are not changed.
Description of development approach
Checking for `state==default` in the right place, and using `FeatureFlagCombo ._getControlCurrentFlag`, not `FeatureFlagCombo._getControlCurrentValue` in `onSave` in audio settings.
Testing strategy:
Manually tested use case from the issue above.
Known issues with pull request:
N/A
